With continuous advances in the wireless communication industry, users can transmit information through radio transmission systems without geographical restrictions. The antenna is an important element in such radio transmission systems. Commonly used antennas include dipole antennas, helical antennas, and the like.
While radio transmission is relatively free from geographical restriction, when the antenna is installed on a location with geographical obstacles (such as corners of walls, ceiling, etc.), its directional gain drops, and the communication quality of signal transmission and reception suffers. To remedy this problem, a common approach is to install a reflection plate on one side of the antenna to enhance the directionality of the antenna, boost the directional gain and improve communication quality.
R.O. C. patent No. 558080 entitled “Dipole antenna equipped with a reflection plate” discloses a reflective dipole antenna. It has a dipole antenna and a reflection plate. The reflection plate has an opening and is spaced from one side of the dipole antenna at a selected distance. The shortest distance between the dipole antenna and the reflection plate is 1/4λ (λ is the wavelength of the frequency spectrum). The reflection plate reflects radiation signals to improve the directional gain of radiation reception and transmission of the dipole antenna.
While the reflection plate can reflect the radiation signals to improve directional gain, it still is not adequate when high directionality is required. Moreover, the reflection plate has to be spaced from the antenna at a selected distance (¼λ), causing difficulty in assembly. Hence how to improve the directionality of the antenna and facilitate convenience of assembly have become issues to be resolved.
Refer to FIG. 1 for a conventional antenna 10 that adopts a series feed network design. Such a design is applicable only in a selected and narrow frequency spectrum (such as 4.9˜5.0 GHz, U-NII-One/Two 5.15˜5.35 GHz, U-NII-Three 5.725˜5.875 GHz). It cannot be used with radio communication that covers multiple frequency spectrums (such as 4.9˜5.875 GHz). In such a situation, two or more antennas have to be used. Hence to increase the antenna transmission bandwidth to free users from procuring additional antennas is also is an issue to be addressed.